"It's impossible to keep a secret ...Especially one as wonderful as this," wrote Preston, who is three months pregnant and due in November, on her official website. The couple also has a 10-year-old daughter Ella Bleu.

"A lot of parents do wish to have another child to come to terms with the loss," she said. "After they've accepted the loss, it's a very natural part of life and can be a very healing thing to do."

"When they do this, it's usually with a little bit of sadness and trepidation even when they know it's the right thing for them, and I don't think we should judge them," she said. "When they make that decision, it's a hard one to make and we should primarily support them."

Other psychologists say that having another child so quickly after such a tragic loss can compound the devastation, leaving the grief process unresolved.

The wife of new British Prime Minister David Cameron and his wife Samantha are also making plans for a new baby, due in September. Their disabled son Ivan died at age 6 in February of 2009.

"The timing is obviously not absolutely ideal but we were very keen to have another baby after Ivan died and sometimes it takes a while before the stork drops one down the chimney," the Conservative politician told the Sun newspaper earlier this year. "But how difficult is it to cope with a new baby after the death of a beloved child?"

Though the couple had daughter Cate, who was 14 at the time, they went on to have two other children: Emma in 1998 and Jack in 2000.

"Nothing in my life has ever hit me and stripped everything away like my son's death," Edwards wrote in his 2004 book, "Four Trials."

Psychologists say that the grief of bereaving parents is the most intense of all sorrows and the most complicated.

"In Western culture, all feelings of hope and meaning and expectations are projected on to the child," said Therese Rando, a Rhode Island psychologist who wrote, "How to Go on Living When Someone You Love Dies"

Overcoming that grief can be difficult, especially if parents remember times they were angry with the child.

"When we lose a child, we feel our expectations are violated," said Rando.

"It's like losing a lung, it's so central," she said. "There is more guilt, more anger and more shattered pain, and other people in society are terrified of you because if it can happen to your child, it can happen to mine."

As the child's protector, we have "basically failed at the task" if a child dies, according to Rando. "We are assaulted. There is a sense of powerlessness and inability to carry out our role as parents."

Have a Subsequent Child, Not a Replacement

Having another child after the "work of grieving" is over, can be a good idea, but not to replace the loss.

"The new pregnancy should not be an attempt to deal with the sadness," she said. "They will see this new little person as a distinct member of their family."

As for the Travoltas, "We would want them not to forget Jett, he will always be an absent member of the family," said Rando. "But the new baby should not feel he has to be Jett."

While it is healthy to have a "subsequent child," it is not psychologically wise to have a "replacement child," said Rando, "imposing the dead child's identity" on the new baby.

Such was the case wth Angel Renee Smith, not her real name, who was born after the death of her older sister Renee and given her middle name.

According to Gerald P. Koocher, dean of the School of Health Sciences at Simmons College in Boston and an expert in the psychology of death, the dynamics of having replacement child range from "healthy" to "bizarre."

"Angel grew up with the persistent knowledge that she had replaced a sister she had never known," said Koocher.

"Angel is now a practicing psychologist, one of my former students, and very well adjusted, although she got into psychology in part because she thought that the naming was a bit creepy and wanted to understand what her mom was going through."

But having another child can sometimes fulfill the dreams of a complete family.

"Because that person is gone, you don't replace that person," he said. "I have formed a family and always had an image of a family with so children and now something bad has happened. After I had it taken away, I still want to have a family with two children and I can make that happen by having another child."

"It's like saying, 'If my wife died, I will get a replacement wife.' I like being married and living in that setting," said Paulson.

Gossip columnists have speculated that Kelly Preston, who is past her fertile prime, sought "help" to get pregnant. Reporter Paula Froelich said the couple likely made a "concerted effort" to have another child.

Travolta publicist Paul Bloch of the Los Angeles agency Rogers and Cowan had no comment on whether Preston had in vitro fertilization with an egg donor. The couple had told People magazine that they were thinking of having a third child as far back as 2007.

"The biological clock is nearly over at the age of 47," said Paulson. "Usually you can get pregnant on your own, it does happen. But it's not very probable."

The oldest woman who ever conceived with her own eggs was 57 and is recorded in Guinness World Records, according to Paulson. In his clinic, the oldest such pregnancy was 45.

"If [Preston] came to me with regular periods, I would say, 'Go try on your own.' After that, then go to egg donation. No other medical intervention is a proven success at 47, but that doesn't mean it's impossible."

Paulsen said he had worked with many patients seeking another pregnancy after the death of a child, but "not so quickly" as Preston and Cameron.

"People variously go through the grieving process and try to figure things out," he said. "It's fair to wait a reasonable amount of time, at least a year, and as the grief passes and you learn to live with the fact the person is gone, you can start looking forward."

Travolta Dogs Killed, Adding to Grief

"Kelly Preston's pregnancy is a huge shocker," said Heidi Parker of Star, who broke the story. "It's a big deal in Hollywood because it's almost like the perfect movie; they had a terrible loss now they're having a miracle in their lives."

"They've suffered a lot in the last year," she said. "They've been grieving. They've had a very difficult time."

Other parents who have lost children say the grief really never does go away, regardless of subsequent pregnancies.

'I am so grateful to have two healthy boys but you never get over the death of a child," she told Britain's Daily Mail newspaper. "When you carry them for nine months, you are planning their future and thinking about their name and how they will fit into the family."

'On Ava's second birthday, I sang happy birthday to her picture," she said. "I will never watch my little girl go to school. Losing a child is like losing part of yourself. You learn to live with it but you never get over it.'